Chapters, DVD subtitle palette, MKV track flags, progress total_bytes

Chapters:
- MPLS PlayList marks parsed (mark_type 1 = chapter)
- Chapter struct on DiscTitle (time_secs, name)
- MKV Chapters element with EditionEntry/ChapterAtom per mark
- 3 MPLS mark tests + 2 MKV chapter tests

DVD subtitle palette:
- IFO palette extraction (PGC offset 0xA4, 16 × YCbCr colors)
- YCbCr→RGB conversion for VobSub .idx format
- DvdSubParser codec_private returns formatted palette
- codec_data field on SubtitleStream flows through pipeline
- 5 palette tests (YCbCr conversion, formatting, overflow)

MKV track flags:
- FlagDefault: primary video/audio = 1, secondary = 0
- FlagForced: forced subtitles = 1
- Language: set from stream language code
- Already implemented, verified with 4 new tests

Progress total_bytes:
- IOStream trait: total_bytes() -> Option<u64>
- DiscStream, IsoStream: from disc_title.size_bytes
- M2tsStream, MkvStream: from file metadata on open
- NetworkStream, StdioStream, NullStream: None

316 tests total, all passing.

src/mux/m2ts.rs

@@ -25,6 +25,8 @@ pub struct M2tsStream {
     disc_title: DiscTitle,
     mode: Mode,
     finished: bool,
+    /// Content size in bytes (file size minus header), set for read mode.
+    content_size: Option<u64>,
 }
 
 impl M2tsStream {
@@ -37,6 +39,7 @@ impl M2tsStream {
                 header_written: false,
             },
             finished: false,
+            content_size: None,
         }
     }
 
@@ -50,14 +53,21 @@ impl M2tsStream {
     ///
     /// Tries FMKV metadata header first. Falls back to PMT scan + PTS duration.
     pub fn open(mut reader: impl Read + Seek + 'static) -> io::Result<Self> {
+        // Get total file size for progress tracking
+        let file_size = reader.seek(SeekFrom::End(0))?;
+        reader.seek(SeekFrom::Start(0))?;
+
         // Try FMKV metadata header
         if let Ok(Some(m)) = meta::read_header(&mut reader) {
+            let header_end = reader.stream_position()?;
+            let content_size = file_size.saturating_sub(header_end);
             return Ok(Self {
                 disc_title: m.to_title(),
                 mode: Mode::Read {
                     reader: Box::new(reader),
                 },
                 finished: false,
+                content_size: Some(content_size),
             });
         }
 
@@ -89,6 +99,7 @@ impl M2tsStream {
                 reader: Box::new(reader),
             },
             finished: false,
+            content_size: Some(file_size),
         })
     }
 }
@@ -109,6 +120,10 @@ impl IOStream for M2tsStream {
             Ok(())
         }
     }
+
+    fn total_bytes(&self) -> Option<u64> {
+        self.content_size
+    }
 }
 
 impl Write for M2tsStream {